We propose to continue studies of the ultrastructure of the two distinct auditory end-organs in macaques, the inner and outer hair cell systems. Further elucidation of their differences in connectivity, and especially of their possible interaction in the organ of Corti, will be attempted. The functional significance of the double hair cell system of the organ of Corti in mammals is a key problem of auditory physiology, but as yet there is no real understanding. In addition to analysis of normal monkeys, we shall take advantage of the selective destruction of outer hair cells by di-hydro-streptomycin to sort out the neural components which are associated with each hair cell system.